Flange connections are used in a variety of industries and a variety of situations to connect meter run sections together, to connect pipe sections together and to connect valves together in Christmas trees used in oil and gas wells and other applications. A flange connection comprises a pair of essentially identical flanges or discs having a series of bolt holes arranged in a circle near the circumference. Each flange is typically welded to one end of a valve or one end of a pipe section. Conventionally, an all-thread bolt is passed through the bolt holes and conventional nuts compress the flanges together captivating a seal or gasket between the flanges thereby making the connection pressure tight.
Some of the equipment having flange connections is very expensive, such as high pressure valves in Christmas trees used to control the flow of oil or gas from hydrocarbon wells, pipeline valves, meters and meter runs and the like. Much of this type equipment is located in remote rural areas where there is little or no security. Consequently, there is always a risk this equipment can be stolen and either sold as scrap to a recycling yard or to used equipment dealers.
It is accordingly not surprising that several approaches have been suggested in the prior art to secure flange connected equipment against theft as shown in U.S. Pat. Nos. 4,300,373; 4,405,161; 4,480,513; 4,537,543; 4,541,256; 4,571,966 and 6,644,075.